System for the remediation of highly contaminated soils

Abstract

A low-temperature thermal desorption (LTTD) system remediates highly contaminated soils. The system (1) reduces the concentration of vaporized contaminants exhausted from the primary treatment unit (PTU) and (2) precisely controls the concentration of vaporized contaminants exhausted from the PTU so as to permit the safe oxidization of contaminants in a secondary treatment unit without oversizing the secondary treatment unit or the baghouse. The concentration of vaporized contaminants exhausted from the PTU is reduced by drawing the vaporized contaminants into a low-pressure region of the PTU so as to contact the burner flame and by supplying this area of flame contact with a modulated supply of air to oxidize a designated portion of the vaporized contaminants within the PTU. The concentration and temperature of the remaining vaporized contaminants are controlled by monitoring the concentration of the contaminants in the gas stream exhausted from the PTU, by calculating a lower explosive limit (LEL) of the contaminant concentration, and by providing a modulated supply of heated dilution air to the gas stream to precisely reduce contaminant concentration levels in the gas stream to a desired percentage of the calculated LEL.

We claim: 
     
       1. A system for the remediation of highly contaminated soil, comprising: a primary treatment unit having a contaminated soil inlet, a remediated soil outlet, and an exhaust gas outlet;   a burner which heats the interior of said primary treatment unit to vaporize contaminants in said soil; and   an air injection system which injects air into said primary treatment unit between said inlet and said outlet so as to oxidize at least some of said vaporized contaminants within said primary treatment unit.   
     
     
       2. A system as defined in claim 1, wherein said air injection system comprises: a blower;   an injector located in said primary treatment unit;   a variable restriction damper which controls the flow of air from said blower to said injector; and   means for varying the amount of restriction provided by said damper.   
     
     
       3. A system as defined in claim 2, wherein said means for varying comprises a motor which is connected to said damper;   a first sensor which monitors the flow of air from said blower towards said injector;   a second sensor which monitors the rate at which contaminated soil is fed into said primary treatment unit; and   a controller which receives signals from said first and second sensors, said controller including means for determining an optimum flow rate of air to be supplied to said injector and for transmitting a signal to said motor to set the amount of restriction provided by said damper to provide said optimum air flow rate.   
     
     
       4. A system as defined in claim 1, wherein said air injection system comprises a manifold non-rotatably mounted within said primary treatment unit and a plurality of nozzles ejecting air from said manifold into said primary treatment unit. 
     
     
       5. A system as defined in claim 4, wherein said air injection system further comprises a shield which shields said manifold from said burner. 
     
     
       6. A system as defined in claim 4, further comprising a cylinder which is mounted in said primary treatment unit proximate said nozzles, which presents an open interior receiving flames from said burner and air from said nozzles, and which presents an exterior directing eddy currents, formed between said cylinder and an inner periphery of said primary treatment unit, towards said burner. 
     
     
       7. A system as defined in claim 1, further comprising a cylinder which is mounted in said primary treatment unit and which presents an open interior receiving flames from said burner and which presents an exterior directing eddy currents, formed between said cylinder and an inner periphery of said primary treatment unit, towards said burner. 
     
     
       8. A system as defined in claim 1, wherein said primary treatment unit comprises a rotary drum having said contaminated soil inlet and said exhaust gas outlet located proximate a first end thereof and said remediated soil outlet proximate a second end thereof. 
     
     
       9. A system as defined in claim 8, wherein said drum is a counterflow drum the second end of which receives heat from said burner. 
     
     
       10. A system as defined in claim 1, further comprising a secondary treatment unit which oxidizes gases exhausted from said exhaust gas outlet of said primary treatment unit;   means for supplying dilution air to said exhaust gases;   means for (1) sensing the level of contaminants in said exhaust gases,   (2) calculating a lower explosive limit of said exhaust gases, and for   (3) determining a flow rate of dilution air required to maintain the level of contaminants in said exhaust gases below a percentage of said lower explosive limit; and     means for controlling said means for supplying so that said determined flow rate of dilution air is supplied to said exhaust gases.   
     
     
       11. A system as defined in claim 10, wherein said means for sensing comprises a flame ionization detector. 
     
     
       12. A system as defined in claim 10, wherein said means for supplying comprises a variable restriction damper and a motor which is actuated by said means for controlling to control the degree of restriction provided by said damper. 
     
     
       13. A system for the remediation of highly contaminated soil, comprising: a primary treatment unit which vaporizes contaminants from said soil, said primary treatment unit having a contaminated soil inlet, a remediated soil outlet, and an exhaust gas outlet;   means for supplying dilution air to gases exhausted from said primary treatment unit; and   means for controlling said means for supplying so as to supply a flow rate of dilution air to said gases at a designated temperature.   
     
     
       14. A system for the remediation of highly contaminated soil, comprising: a primary treatment unit which vaporizes contaminants from said soil, said primary treatment unit having a contaminated soil inlet, a remediated soil outlet, and an exhaust gas outlet;   means for supplying dilution air to gases exhausted from said primary treatment unit;   means for (1) sensing the level of contaminants in said exhaust gases,   (2) calculating a lower explosive limit of said exhaust gases, and for   (3) determining a flow rate of dilution air required to maintain the level of contaminants in said exhaust gases below a percentage of said lower explosive limit; and   means for controlling said means for supplying to supply said determined flow rate of dilution air to said exhaust gases at a designated temperature.     
     
     
       15. A system as defined in claim 13, further comprising a burner which heats the interior of said primary treatment unit to vaporize contaminants in said soil; and   an air injection system which injects air into said primary treatment unit between said inlet and said remediated soil outlet so as to oxidize at least some of said vaporized contaminants within said primary treatment unit.